Question 11
The following table gives information on the proportions of a population that have been exposed to a risk factor for a disease and then subsequently developed the disease.
Exposure + Indicates the proportion exposed to the risk factor (A+B)
Exposure  Indicates the proportion not exposed to the risk factor (C+D)
Disease + Indicates the proportion that subsequently developed the disease (A+C)
Disease  Indicates the proportion that did not subsequently develop the disease (B+D)
Disease + 
Disease  

Exposure + 
A 
B 
Exposure  
C 
D 
Define prevalence AND, with reference to A, B, C, D in the table above, give the prevalence of the disease in this population. (20% marks)
Define relative risk (RR) AND, with reference to A, B, C, D in the table above, derive the relative risk Of developing the disease after exposure to the risk factor. (40% marks)
Define attributable risk (AR) AND, with reference to A, B, C, D in the table above, give the attributable risk of exposure to the risk factor on developing the disease in this population. (40% marks)
a) Prevalence: number of event (e.g. disease) in a specific population at a particular time point.
Prevalence of the Disease in this population:
A+C / (A+B+C+D)
b) Relative risk is the ratio of the probability of an event occurring (e.g. developing a disease) in an exposed group to the probability of the event occurring in a comparison, in nonexposed group
[A / (A+B) ] / [ C / (C+D)]
c) Attributable risk is the difference in the rate of a condition between an exposed and unexposed population.
A/ (A+B)C/(C+D)
This is another SAQ which makes it very easy to earn high marks, as it asks for unambiguous memorised definitions and has a clearcut right answer.
Somebody got 9.2.
Prevalence:
Relative risk:
This is the difference in event rates between 2 groups expressed as proportion of the event rate in the untreated group. The slightly broken English of the college answer probably comes from an article similar to the 2017 article by Tenny et al, and was probably meant to say "relative risk is a ratio of the probability of an event occurring in the exposed group versus the probability of the event occurring in the nonexposed group."
Attributable risk: